The generation of electrical energy with the aid of photovoltaics is increasingly gaining in importance. A multiplicity of decentralized power generation installations of this type have been installed globally in the meantime, wherein the typical supply power as an essential characteristic feature of these installations is increasing at the same time. Particularly in the case of a high supply power, it is customary to interconnect a large number of PV modules in series to form a so-called string, which is connected to the inverter. As a consequence, high DC voltages are present on the input lines of the inverter during operation. In order to prevent the formation of arcs inside the inverter housing, which would lead to damage or destruction of the inverter, sufficient isolation distances are provided between the voltage-carrying conductors. Nevertheless, arc events in inverters occur from time to time, which in the extreme case can lead not just to the destruction of the inverter, but as a consequence also to fires if the effects of the arc do not remain restricted to the interior of the housing. Therefore, for safety reasons, solid metal housings (sheet-metal or die-cast housings) are usually used which, over a certain time duration, can limit these effects of a burning arc to the housing interior, but which also make up a high proportion of the production costs.
Arcs are often triggered by the fact that sufficient moisture has accumulated in the interior of the inverter, such that along the surfaces creepage paths between the voltage-carrying components can form which can bridge the isolation distances. When voltage is present creepage currents flow along the creepage paths which can intensify to form arcs or cause corrosion which in turn, on account of an increase in contact resistances, can lead to consequential problems such as device failures or contact heating through to fire. Experience shows that even in the case of housings in which the interior is protected by a high protection class against external influences, for example by the protection class IP65 customary in the case of inverters, moisture can accumulate in the interior over the course of time. This is frequently caused by a pressure equalizing element which compensates the volumetric change of the air in the housing caused by temperature fluctuations, by exchanging air with the surrounding environment. Through the pressure equalizing element, moist ambient air can pass into the housing, with the result that relatively large quantities of moisture accumulate in the housing interior over the course of time even when direct entry of water does not take place.
The document WO 2004/040724 discloses a switchgear cabinet for electronic devices such as computers, the climate values of which such as temperature and air humidity are monitored and actively influenced. However, this technical teaching can be applied only to a limited extent to inverters, whose air-conditioning possibilities for their housing interior are limited. At the same time, diverse documents exist which describe apparatuses and methods where PV generators are electrically disconnected from the inverters and/or short-circuited if a hazard situation (such as a fire, an arc and an overheating) is detected. By way of example, reference is made to the document DE10 2006 060815 at this juncture. What is disadvantageous about these solutions is that the measures are initiated only after the occurrence of the damaging event.
Furthermore, the document DE102009013311 discloses a control unit of a wind power installation equipped with temperature and moisture sensors in order to protect the control unit against overheating or corrosion. In addition, the document DE102007054215 discloses such wind power installations equipped with a preheating device that preheats the temperature critical components to operating temperature before the wind power installation is started up. In both cases, the installation generates no energy as long as the temperature and/or the moisture values are not in a desired range.